This invention relates to a process for recovering tungsten and rhenium from a relatively impure tungsten and rhenium solution. More, particularly, it relates to a process for recovery of tungsten and rhenium from an impure solution by removing the tungsten from the solution as a solid with hexamine.
In a process for recovering the metal values from tungsten-rhenium alloy scrap, an alkaline solution containing sodium tungstate and sodium perrhenate is generally formed. A separation of the two metals is necessary before purification and metal preparation steps can be initiated.
Prior separation techniques include extraction of rhenium by means of a strongly basic ion exchange resin, precipitation of tungstic acid, and the preferential volatilization of rhenium heptoxide.
Disadvantages of the ion exchange method include the difficulty of stripping rhenium from the resin, the inefficiency of separation should a high concentration of certain ions such as chloride be present, and the necessity of having large scale specialized equipment available.
Disadvantages of the tungstic acid technique include an incomplete precipitation of tungsten under desired operating conditions, leaving an appreciable tungsten content in the rhenium portion and the requirement of production equipment suitable for handling very corrosive hot hydrochloric acid needed for the tunstic acid precipitation process.
The process for oxidizing the scrap and subliming the rhenium heptoxide has the disadvantage of incomplete removal of the rhenium from the tungstic oxide, and the requirement of specialized furnace equipment to be designed and built.
A process for efficiently recovering rhenium and tungsten without specialized equipment would be an advancement in the art.